What Is the Cornea?

The transparent part of the front part of the outer layer of the eyeball wall. It is circular and occupies one-sixth of the outer area and is about 1 mm thick. It is mainly composed of non-vascular connective tissue. The front is slightly protruded, curved like a sphere, and has a refractive effect. The cornea is rich in sensory nerve endings. Any minor irritation, injury or inflammation can cause pain and tears. If you touch the cornea with cotton, it will cause a protective response to the cracked eyes, called corneal reflex. The connecting part of the cornea and sclera is called the limbus. Corneal blood vessels and aqueous humor in the eyeballs provide corneal nutrition. The curvature of the normal cornea is the same, so the refractive index is the same. If the curvature is not uniform, it will cause abnormal refraction, called astigmatism.

The 1 / 6th non-vascular transparent fiber membrane located at the front of the eyeball wall is called cornea. The normal cornea is highly transparent, with a smooth surface, convex and concave front, shaped like a convex-concave lens, and the edge connecting with the sclera-like case. It is circular from the back and horizontally from the front. This is because the upper and lower edges of the anterior cornea are covered by the sclera and conjunctiva stretch more than the horizontal sides. The cornea is divided into a corneal base and a limbal cornea. Histologically, it is divided into five layers from front to back: epithelial cell layer, preelastic layer, matrix layer, posterior elastic layer and endothelial cell layer. However, the tear film, epithelium, anterior elastic layer, matrix, posterior elastic membrane, and endothelium can be seen under a slit lamp biomicroscope.

Also known as eye capsule, outer wall of eyeball. That is, the outer part of the eyeball has the functions of protecting the content of the eye and partially transmitting light, light, and light, and maintaining a certain shape of the outer membrane wall. It is anatomically divided into three layers from the outside to the inside: the outer layer is a fibrous membrane, including the front 1/6 transparent cornea and the back 5/6 opaque sclera, which is tough and protects the tissues inside the eyeball: the middle layer is the uveal membrane, including the iris, The ciliary body and choroid are rich in blood vessels and pigments, and have the function of nourishing the internal tissues of the eye, shielding and regulating light; the inner layer is the retina, an important tissue that senses light stimulation and conducts nerve impulses.

The eyeball wall is divided into three layers.

Outer layer:

The outermost layer of the eyeball wall is an adventitia, also called a fibrous membrane, which plays a supporting and protecting role on the eyeball and has a refractive effect. Divided into cornea and sclera.

The cornea is located in the front, occupying 1/6 of the adventitia. It is colorless and transparent, has large curvature, and has a refractive effect. There are rich sensory nerves in the cornea, which are very sensitive. It will feel very uncomfortable or painful when small things enter the eyes or there is inflammation or trauma. It reminds you to deal with it quickly. The sclera occupies the last 5/6 of the adventitia, is milky white, opaque, very tough and protective.

Middle:

The middle layer of the eyeball wall is the middle membrane, also known as the vascular membrane, which contains a large number of pigment cells and blood vessels, and has nutrition and light shielding effects. It is also divided into three parts: the front is the iris, and the round hole in the center of the iris is the pupil we often hear. The pupil is equivalent to the aperture, which controls the amount of light entering the eyeball (when the light is strong and the thing you are looking at is closer) , Pupils shrink; pupils dilate when the light is weak and what is seen far away); behind the iris is a circular ciliary body that can produce aqueous humor and can adjust the curvature of the lens; the rear 2/3 of the media The choroid, which is rich in blood vessels and pigment cells, is equivalent to a camera's dark box, shielding the diffuse light that enters the eye through the sclera, and at the same time provides nutrition to the retina.

Inner layer:

The inner layer of the eyeball wall is the retina, which is an important part of light sensitivity, which is equivalent to the negative of a camera. There are cone cells and rod cells in the retina. Cone-shaped cells can feel the stimulus of bright light and color during the day. Problems with cone-shaped cells can cause color blindness or color weakness; rod-shaped cells can receive dark light stimulation, which can cause night blindness when problems occur.